Resize Oracle Datafile的脚本

转自惜总文章:http://ask.orasos.com/thread-11-1-1.html

set verify off
column file_name format a50 word_wrapped
column smallest format 999,990 heading "Smallest|Size|Poss."
column currsize format 999,990 heading "Current|Size"
column savings  format 999,990 heading "Poss.|Savings"
break on report
compute sum of savings on report

column value new_val blksize
select value from v$parameter where name = 'db_block_size'
/

select file_name,
ceil( (nvl(hwm,1)*&&blksize)/1024/1024 ) smallest,
ceil( blocks*&&blksize/1024/1024) currsize,
ceil( blocks*&&blksize/1024/1024) -
ceil( (nvl(hwm,1)*&&blksize)/1024/1024 ) savings
from dba_data_files a,
( select file_id, max(block_id+blocks-1) hwm
from dba_extents
group by file_id ) b
where a.file_id = b.file_id(+)
/

column cmd format a75 word_wrapped

select 'alter database datafile '''||file_name||''' resize ' ||
ceil( (nvl(hwm,1)*&&blksize)/1024/1024 )  || 'm;' cmd
from dba_data_files a,
( select file_id, max(block_id+blocks-1) hwm
from dba_extents
group by file_id ) b
where a.file_id = b.file_id(+)
and ceil( blocks*&&blksize/1024/1024) -
ceil( (nvl(hwm,1)*&&blksize)/1024/1024 ) > 0

请注意:以上脚本针对如下情况,不能回收全部的空间:

比如一个10个GB的datafile,已经使用第2GB 和第9GB,从表空间使用率的角度看,Free空间是8GB, 用以上脚本仅仅能回收的空间肯定是远远小于8GB.

因为,resize的过程只是缩小Datafile的大小,resize并不负责move数据库对象(table 或者index).

Move的过程是把大号object_id上的row 搬家搬到小号object_id上的过程.